Convection food heating

ABSTRACT

Disclosed are an improved method and apparatus for heating which enables rapid heating of foods to obtain any one of a number of textures. A fried taste, texture and appearance can be achieved without using large amounts of oil or encountering the other disadvantages of frying. 
     According to a preferred embodiment, the form of the apparatus is employed to fry foods using a heat exchange fluid comprising air containing dispersed cooking oil or fat, which performs the disclosed method. A cooking chamber is provided having a reservoir at a low point capable of holding cooking oil. The oil is dispersed into the closed heating chamber as a convective air flow is established within the heating chamber. A rotating support holds the food about an axis accentrically positioned from the axis of an impeller means which disperses the oil or fat and creates a positive flow of air within the chamber, to uniformly contact and fry the food.

RELATED APPLICATION

This aplication is a continuation-in-part of my copending application,U.S. Ser. No. 356,229, filed Mar. 8, 1982, now U.S. Pat. No. 4,439,459,issued Mar. 27, 1984.

TECHNICAL FIELD

The present invention relates to heating, and in particular to a heatingprocess and apparatus which is particularly adaptable to rapid cookingof food to achieve results similar to those obtained by frying in hotoil, and is further adaptable to stir frying, steaming, convectioncooking, slow cooking, and air drying.

Heating devices currently available are in general restricted to heatingin a single mode such as by convection, radiant heat, steam, conductionby a liquid heat transfer medium and microwave energy. Each of thesemethods has its own advantages and characteristic effects when employedto heat food. It would, however, be advantageous to provide a singleapparatus capable of use for frying and a number of other cookingprocesses.

Among the various types of cooked foods, fried foods are especiallyinteresting. They are widely enjoyed. They possess a taste, texture andaroma which cannot be captured by any other heating method due to boththe speed of cooking and the flavors developed by the interaction of hotoil with the food surfaces. Unfortunately, there are a number ofproblems with the use of frying and fried foods which greatly limit theuse of this method. Not the least among these is a general dislike ofthe frying process itself. Other problems relate to the typical mess andcost associated with frying and the potential health problems oftenassociated with fried foods.

The dislike of frying, both deep fat frying and pan frying, is believedto deter large numbers of domestic, non-professional cooks fromfrequently preparing food by these methods. This stems in part from thedangerous and often painful spattering of hot cooking oil and thepotential danger involved in utilizing relatively large volumes ofcooking oil at temperatures typically within the range of from about300° to about 400° F., especially when there are children in thehousehold. A further danger involved with frying is the tendency for theoil to ignite when improperly handled. This dislike is becoming moreprominent as amateur cooks find less time to develop their skills atfrying--in part because there is an increasing proportion of meals beingeaten away from home and in part because of the ever increasing numberof convenience food products which are being made available. Thus, theadvent of alternatives to home frying, including pre-fried frozen foodproducts and a variety of coating mixes which, to some degree, simulatethe characteristics of fried foods, have decreased the frequency of homefrying.

Other oil-related problems also affecting the frequent use of frying toprepare foods at home involve the mess, cost and suspected healthdisadvantages of frying. Typically, frying in an open pan or in a deepfat fryer will result in a film of oil on surrounding surfaces includingthe stove top, counter tops, walls and floor. In addition to the safetyproblems associated with this, it is simply often more work to clean upafter preparing fried foods than is justified by the enjoymentexperienced in consuming them. Moreover, in the case of deep fat frying,large amounts of relatively expensive fat or oil are required. And, thequantity of food prepared at one time is restricted by the size of thefryer. After frying is completed, time must be permitted for the oil tocool, and suitable precautions must be taken to protect the oil againstbecoming rancid during storage. Additionally, the resulting food productprepared in this manner typically contains a high level of fat whichmost people take the time to drain prior to serving for taste as well assuspected health reasons.

While fried foods have not been established as a cause for healthproblems among the general public when consumed in moderation as part ofa balanced diet, various writers have criticized fried foods becausethey contain high levels of fat and because that fat is typically highin cholesterol and saturated fatty acids. Moreover, fat has a highcaloric density and is known as something to be greatly restricted byweight-conscious consumers. The use of cooking fat with a high contentof saturated fatty acid is typical because these fats tend to havehigher smoke points than polyunsaturated oils. And, when employed fordeep fat frying where economics demand the reuse of the oil over severalcycles of cooking, cooling and storing, the fats containing high levelsof saturated fatty acids are also more stable against oxidation and canbe reused over a greater period of time without becoming rancid.

Prominent among other cooking methods is convection heating which, asconventionally performed, has the disadvantage that it relies upon apoor heat conductor--air. Moreover, convection heating has a dryingtendency which necessitates basting for the preparation of many foodproducts. While basting can prevent excessive drying, it demands theconstant attention of the cook throughout the period of preparation.Directly related to the poor heat transfer ability of the air is theextended cooking period which is typically required compared to frying.

An early attempt to solve the problems of prolonged cooking times anddrying of the food product entailed cooking the food in a closed chamberwhich maintained an elevated pressure and temprature due to steam beingretained within the chamber. While this method is faster than convectioncooking and does prevent dryness, it cannot be employed for productswhich require a crispy texture or a browned exterior. For example,products such as french fried potatoes and fried chicken which aretypically prepared by deep fat frying, cannot be prepared by steampressure cooking unless they are immersed in hot cooking oil within thepressure chamber. In the absence of the oil, the products are soggy andunbrowned in appearance and taste and coating materials tend to sloughoff. Thus, steam-convection cooking is also unacceptable for many foods.

Microwave cooking has recently become very popular because of its speedand low energy requirements; however, like steam cooking, it is notcapable of providing a browned surface. Moreover, because it, in effect,cooks from the inside, steam is generated within the product and oftencauses surface disruptions or even a mildly-explosive shattering of thefood. Recently, special microwave ovens have been designed to provideradiant heating in addition to microwave heating to provide a brownedexterior on the cooked food. However, the addition of the browningelement does not alleviate the problem of internal steam generationwhich develops a typical "steam cooked" flavor. Additionally, it isdifficult to achieve uniform heating with microwave ovens. Onedifficulty has been the distribution of the microwave energy within theoven, but this has been solved to some degree by better design. Anotherdifficulty, which has not yet been corrected, is that foods which havevarying textures or thicknesses will often be cooked to varying degreesdue to the varying absorption of the microwave energy. This in manyinstances necessitates employing large amounts of liquid within thecooking vessel within the oven and therefore again diminishes theability to obtain a browned exterior on the cooked product.

Radiant heating has been in wide-spread use for a great number of yearsfor cooking meat and other products which require a browned exterior.This process, however, has the disadvantage that temperature control atthe surface of the food is difficult because the surface will absorbheat more rapidly than it can be dissipated to the surroundings ortransferred to the interior of the product. Accordingly, while cookingby radiant heat, such as by broiling, is an effective method forpreparing particular types of food products such as steaks, it is notpractical in terms of energy consumption and process control for a widevariety of other products. Nor does it provide the hot oil contactrequired to develop a characteristic fried flavor.

Accordingly, there is a present need for an improved method andapparatus for heating food products which provides rapid cooking,efficiency of operation in terms of energy consumption and cookingfluids such as fats and sauces, adaptability to a wide variety of foodmaterials and portion sizes, and the capability of providing browned,crisp, fried-like surface textures for meat products yet being capableof cooking vegetables and fruits without adversely affecting theirdesirable surface textures. There is a need for a cooking apparatuswhich has the capability of frying, stir frying, steaming, convectionheating, slow cooking and air drying.

In a more limited sense, there is a need for an improved process andapparatus for heating food to give the taste, texture, and aromatypically afforded by frying, without the disadvantages normallyassociated with frying. In particular, it would be advantageous toprovide an improved process and apparatus capable of preparing a friedfood which would employ only very limited amounts of fat, would avoidmuch of the mess and danger associated with frying, and would providefried products which would be perceived as more healthful in that theywould have lower residual fat contents and could be prepared with theuse of highly polyunsaturated cooking oils.

It would be further advantageous to have a process and an apparatuscapable of achieving these results which could also be adaptable to theuse of liquid heat transfer media other than triglyceride fats, such aswater and sauces, and would be capable of control in terms of heatintensity to provide a wide variety of tastes and textures in thecompleted food products.

BACKGROUND ART

A number of prior art references have discussed the possibility offrying food products on a commercial scale using limited quantities ofcooking oil. Basically, these disclosures can be classified into twobroad groups. In the first group are those procedures which simulatefrying by coating a food product with cooking oil prior to subjecting itto a separate convection heating step. In the second group are thosepatents which direct a pressurized spray of the oil directly against thefood product.

Representative of the first group of prior art teachings in U.S. Pat.No. 4,269,861 to Caridis et al. According to this disclosure, frenchfried potatos are prepared for freezing and subsequent finish frying toclosely resemble french fried potatos prepared directly from freshpotatos. The process includes the steps of peeling and trimming potatos,cutting them into strips, washing the strips, treating the washed stripswith hot oil for a brief period, subjecting the strips to convectiondrying, again treating them with oil, and finally convection drying themto the desired final moisture content and a fat content of from about 3to 7%. It is disclosed that in certain instances it may be desirable toomit immersing the strips in hot oil and that a substituted hot oiltreatment can be employed. Specifically, it is disclosed that the stripsmay be passed through a curtain or spray of hot oil to achieve thedesired oil pick-up on the potato product before subjecting the productto the hot atmosphere. Thus, while deep fat frying can be simulated bythis process, it requires two distinct process steps: contact with hotoil in one step and contact with heated convection gases in another.

While this process does, to some extent, limit the quantity of oilpicked up on the intermediate product, it is not disclosed as a processfor preparing a completely cooked product. Moreover, the cooking stepsset forth in the examples are disclosed to take about 9 minutes, to befollowed by a subsequent deep fat frying step which takes another 2.5minutes. Thus, much of the advantage of reduced oil pick-up which may beachieved during the preliminary processing would be lost where deep fatfrying is necessitated for final preparation.

Representative of the second group of prior art teachings are BritishPat. No. 621,821 to Crittall Kitchen Equipment Company, Ltd., et al,U.S. Pat. No. 4,134,998 to Liebermann, and U.S. Pat. No. 4,064,796 toJones. According to the British patent, food articles are cooked bydirecting a pressurized spray of heated liquid cooking medium onto foodarticles that are supported in a cooking chamber, rather than byimmersing them therein. While this procedure does somewhat decrease theamount of oil or other liquid heating medium which would be required fortypical frying by immersion, a continuous spray would requiresubstantial amounts of oil, and the pressurized spray of liquid whichdirectly impinges upon the exterior surfaces of the food product wouldtend to dislodge delicate coatings of the type typically employed forchicken and the like. In addition, the continued impingement of the hotoil can cause a continuing disruption of the surface of the food,permitting the exudation of juices from the interior of the food.Moreover, the resulting product would be as saturated with fat asconventionally deep fat fried foods and would also necessitate the useof fats having high levels of saturated fatty acids to inhibitdeterioration of the oil due to oxidation and exceeding its smoke point.Moreover, because all heat is supplied to the process by means of thehot oil, the ability for the oil to heat the food product is rapidlydissipated upon contact with the food and further heating is achievedonly upon contacting the food with additional hot oil. Anotherdisadvantage of the process is that the heating chamber is not sealedand steam generated during the heating process cannot be utilized toimprove heating efficiency.

The disclosure of Liebermann is similar to that in the British patent inseveral regards, but differs principally in that the oil sprays operateat a more highly elevated pressure, disclosed as being between 10 and 70psig. This higher pressure would have the disadvantage that it wouldeven more readily tend to dislodge coatings and continue to disrupt thesurface permitting exudation of food juices than would be expectedaccording to the British patent disclosure. It is similar to that priordisclosure, however, with regard to the other disadvantages.

The disclosure of Jones is again similar to Liebermann and the Britishpatent, but employs sprays from both the top and bottom of the foodunder conditions which provide a tranquil environment.

The use of convection heating is achieving a degree of acceptance for anumber of cooking needs. According to the disclosure of U.S. Pat. No.4,155,294 to Langhammer, cooking is achieved by directing a flow of hotair at food products held within a rotatable cage. However, because thecooking process is "greaselss", the cooking achieved cannot provide atrue fried texture and flavor. Further examples of convection cookersare U.S. Pat. Nos. 4,011,805 to Vegh et al and 4,058,635 to Durth, bothof which inject steam during convection heating. The food productscooked by these devices are even further removed than those ofLanghammer from fried foods in terms of flavor and texture due to thesteam cooking effects of the devices.

Accordingly, while the prior art has recognized that the amount of oilemployed for a commercial frying process can be somewhat limited byimpinging sprays of oil upon a food product, and that forced convectioncooking is faster than oven baking, especially where steam is employed,there is no disclosure of a process or an apparatus which is capable ofhome use to achieve rapid hot oil heating of food products without theinefficiency, mess, cost, and dangers typically associated with fryingfoods. And, there remains a need for such a process and apparatus,especially one which could so improve efficiency, economy and simplicityof operation that consumers would not have to forgo the enjoyment offried foods because of the limitations inherent in current home cookingmethods. Moreover, it would be desirable to provide an improved cookingmethod and apparatus which could provide food products having the taste,texture and aroma of deep fat fried foods but use only a fraction of thenormal amount of oil. This would be more attractive from a healthstandpoint due to lower amounts of residual fat within the cookedproduct and the ability to substitute highly polyunsaturated vegetableoils for the highly saturated fats which are currently required forpractical and economic reasons.

DISCLOSURE OF INVENTION

In accordance with the present invention, I provide an improved processand apparatus for heating food. Heat is transferred from a heat sourceto a food product by circulating a heat exchange fluid. Where a friedtexture is desired, the heat exchange fluid will comprise an oildispersed in air. Other heat exchange fluids can be employed to achievedifferent cooking effects.

In its broad aspects, the process comprises: placing food on a supportrotatable about a first axis within a heating chamber, projecting a heatexchange fluid into contact with the food within the chamber such thatsaid fluid contacts said food accentrically of said first axis, androtating said support about said first axis. While any heat exchangefluid can be employed, preferably it comprises one which is capable ofremaining liquid under the conditions of operation. A triglyceride fatis dispersed in air, the dispersion comprising the heat exchange fluid,in the more preferred aspects of the invention, and provides a productwhich has the taste, texture, and aroma attributes of deep fat friedfoods.

The apparatus, in one of its broad aspects comprises: a support meansfor holding material to be heated, means for creating a flow of hot airin proximity to the support means, and means for introducing a dispersedheat exchange medium into the air within the chamber. According toanother aspect of the apparatus, a support means for holding material tobe heated is rotatably mounted in a heating chamber about a first axis,and an impeller means for directing heat exchange medium into contactwith the material to be heated is rotatably mounted about a second axiswithin the chamber.

Thus, the invention provides fundamentally new concepts of heating. Theability to achieve a fried texture according to the invention has, as acentral feature, the introduction of oil into a convective air flow toimprove heat transfer and increase the speed of cooking while providingintimate oil contact with the food for optimum flavor development. Aswill be apparent from the description of the various embodiments of theinvention which will follow, the convection within the heating chambercan be created in any manner effective to provide a relative movementbetween the air and the food maintained within the chamber. This can beachieved by forcing a flow of air past a stationary support meansholding the food, by rotating the support means holding the food withina chamber having no otherwise forced convection, or by a combination offorcing a flow of air past the support means and simultaneously rotatingthe support means.

The more preferred aspects of the invention provide separate,accentrically positioned axes for rotating the food support and theimpeller means for directing air-dispersed-oil or other heat exchangefluid into contact with the food. The accentric flow thus achievedprovides more even contact with the food. It minimizes dead spaces andhot spots, providing a better-quality product. Moreover, the ability toseparately power both the support and the impeller means enables manyvariations in the cooking process. For example, the use of high velocityair containing dispersed fat, permits velocities sufficiently high toactually stir foods such as cut vegetables and the like during cooking.The product is stir fried by this technique. Also, it is possible tofill the chamber with an aqueous sauce or gravy and slow cook a food byslow rotation of the impeller means.

And as will become apparent, the ability to rotate the support meanswithin the chamber at high speeds provides a desirable manner forrapidly and easily removing excess cooking oil or other liquid heatexchange medium from the cooked food product. An additional feature ofthe invention is that the heating chamber can be sealed, if desired, toprovide the advantages of more rapid pressure cooking in combinationwith the convective heating which is enhanced through the introductionof dispersed hot heat exchange medium therein.

It will also become apparent that the advantages of deep fat frying andpan frying can be achieved without the danger, mess, expense and healthproblems normally associated with these kinds of cooking. In particular,the invention permits the use of very small amounts of cooking oil orother heat exchange medium in place of the large amounts of fat whichare typically employed. Additionally, because the heating chamber can beclosed, no spattering or splashing of the heat exchange medium outsideof the chamber can occur. Moreover, when designed according to the morepreferred aspects of the invention, the clean-up of the apparatus aftercooking is simply accomplished by immersing a limited number ofremovable parts into hot, soapy water. And, the resulting food productsare rapidly cooked almost as fast as deep fat frying due to thecombination of heating effects. The food products are perceived as beingmore healthful because of the ability of the invention in its morepreferred aspects to remove excess oil and to employ highlypolyunsaturated vegetable oils as the liquid heat exchange medium.

In addition to all of these advantages, the apparatus is yet furtherattractive from the standpoint of practicality because it can be simplycontrolled for cooking a wide variety of foods, including meat,vegetables and fruits, and is adaptable to different specific types ofcooking such as stir frying, convection cooking, steaming and the use ofsauces or other basting liquids instead of oil.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood and the above advantagesand others will become more apparent when the following detaileddescription is read in light of the accompanying drawings wherein:

FIG. 1 schematically illustrates, partly in section, a simplifiedapparatus according to the present invention;

FIG. 2 schematically illustrates, partly in section, a more preferredembodiment of the invention wherein the heating chamber is closed andthe air and oil are recycled;

FIG. 3 schematically illustrates, also partly in section, an embodimentof the invention wherein the chamber is closed and the convective flowof air is created by rotating the support within the chamber which holdsthe food;

FIG. 4 is an exploded view in perspective which illustrates a preferredapparatus according to the invention;

FIG. 5 is a cross-sectional view of the apparatus shown in FIG. 4; and

FIG. 6 is a front-elevation, partially in section, showing a preferredform of the apparatus which provides flow of heat exchange fluid from animpeller, accentrically positioned relative to the food support means.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one of the simplest forms of apparatus according tothe invention. This figure, partly in section, shows a frying pan 10forming the lower portion of a heating chamber, the upper portion beingformed by conical partial cover 12. A foraminous support 14 ispositioned at the bottom of the pan 10 for holding articles, such aspotatos, chicken, or the like, for heating. The support 14 is preferablymade of a stainless steel wire mesh, but can be of any other suitableconstruction so long as it permits air to flow through from top tobottom. The partial cover 12 can be constructed to stand at the bottomof pan 10 or to be otherwise supported such as by arms which extendradially from the bottom of the cover 12 for resting upon the top of thepan 10. Where desired, the pan 10 can be placed upon a heated surfaceor, more typically, it is placed upon an unheated surface.

Reservoir 16 maintains a suitable supply of liquid heat exchange mediumsuch as a triglyceride cooking oil for delivery to the heating chamberby means of delivery pipe 18 and nozzle 20. The nozzle 20 is preferablyconfigured to provide a fine dispersion of liquid heat exchange mediumwithin the heating chamber, but can be arranged to simply drip theliquid medium into the chamber for fine dispersion by a rapidly movingflow of hot air.

The flow of air for the embodiment of FIG. 1 is created by a hot airgenerator shown generally as 22. Air inlet ports 24 permit room air tobe drawn into a blower maintained within the generator 22 and to beforced through channel 26 toward the support 14. An electricalresistance heater 28 is positioned within channel 26 to heat the air asit is blown therethrough. The air heats the liquid medium beingdispersed by nozzle 20 and carries it into contact with the articlesmaintained on support 14 for heating.

The liquid heat exchange medium can be any material which is liquidunder the conditions of use. Typically, the medium will be atriglyceride fat of either vegetable or animal origin or blends thereof.Where desired, the triglyceride fat can be a normally-solid fat such aslard, margarine or butter which is liqufied prior to placing into supplychamber 16. Preferably, however, the triglyceride fat will be a liquidvegetable oil, and most preferably one which is high in polyunsaturatedfatty acids, such as sunflower oil, corn oil or safflower oil. It is anadvantage of the present invention that these highly polyunsaturatedoils can be employed with good results. In some cases, a foam reducingadditive may be helpful.

The temperature of the hot air supplied by means 22 is preferablycontrolled, by means not shown, to be within the temperature range offrom about 250° to about 450° F. which will provide rapid heatingwithout degradation of either the articles to be heated or the oilemployed. It is an advantage of the invention that temperatures wellabove the smoke point of the triglyceride oil can be employed withoutadverse flavors being developed, because the oil remains at the elevatedtemperatures only for limited periods of time and is rapidly cooled uponcontact with the articles being heated.

An apparatus similar to that shown in FIG. 1 was employed in alaboratory cooking test. According to this test, a regular frying panformed the base of the system. Food was placed on a wire mesh standwithin the frying pan. A typical laboratory heat gun similar to thatshown in the drawing was mounted above the frying pan. Between the panand heat gun, a partial frying pan cover was used to direct the airflow. An oil supply system including an oil reservoir and a narrow tubedripped oil into the air stream from the heat gun. The rapidly movinghot air turned the droplets of oil into a fine mist which was delivereddirectly onto the food by the stream of hot air. The air flowed past thefood through the mesh stand and out through the openings between the panand the partial cover into the ambient air. Some of the oil collected onthe food and then dripped into the bottom of the pan. This operationcooked chicken very rapidly and delivered a typical fried appearanceemploying a very limited amount of oil. While this example illustratesthe effectiveness of the present invention, it is not the preferred modeof operation because much of the energy supplied to heat the air is lostas the air is exhausted into the room. Additionally, this embodimentdoes not eliminate the problems of oil mess normally associated withfrying foods, because a portion of the oil exits the pan with the air.

FIG. 2 schematically represents a simplified apparatus which remediesthe two principal difficulties with the apparatus shown in FIG. 1. Thus,the apparatus shown in partial section in FIG. 2 provides means forrecirculating both the oil and the air. The parts in FIG. 2 will benumbered with 3-digit numbers greater than 200. Those parts which arethe functional equivalents to similar parts in FIG. 1 will have the samelast two digits as the like part in FIG. 1. For example, heating chamber210 is essentially equivalent to the pan 10 in FIG. 1 in that it holdsthe foraminous support means 214 which holds the food or other articlesto be cooked.

At the top of heating chamber 210 is a conically-shaped upper chamberportion 212 where heated process air enters the chamber 210. At thebottom of chamber 210 is a reservoir 216 for holding a supply of liquidheat exchange medium for the process. Prior to starting the apparatusinto operation, the reservoir 216 is supplied with an appropriatelysmall amount of liquid medium which is circulated through line 218 tothe liquid dispersion means 220 by means of a pump or other circulatingdevice 232. The dispersion means 220 can have a plurality ofradially-extending conduits 221 each terminating with one or moreorifices to disperse the oil. If desired, the conduits 221 can havefurther orifices along their radial extents to provide additionaloutlets for the liquid medium.

Hot air generator, shown generally as 222, will draw air from theheating chamber 210 by means of conduit 230 and direct the air throughconduit 226 which has an electrical resistance heating element 228positioned therein. Means 228 will heat the air as it is passed throughconduit 226 prior to directing it past the oil dispersion means 220which continuously introduces finely dispersed liquid heat exchangemedium into the air. The air is then drawn through the support 214containing articles to be heated and recirculated through line 230 tothe process. Because the cover 212 permits sealing the heating chamber,heating can be conducted under a positive pressure to achieve more rapidcooking.

A portion of the liquid heat exchange medium will contact the articlesmaintained within support 214 and provide heat transfer thereto. Aportion of the liquid medium, however, will remain in the air stream asit is being recirculated through the hot air generator 222 by means ofconduit 230 for recontact with the article to be heated on the next paththrough the heating chamber 210. If desired, a filter element, notshown, can be employed within conduit 230 to condense the oil, prior toreheating, either for discarding upon termination of the process or forreturn to the reservoir 216 for recycling to the process.

The amount of oil employed will preferably be sufficient to permitcomplete wetting of the food or other articles held within the support214 and result in dripping from the articles through screen 215 forcollection in reservoir 216. Screen 215 prevents any solid particulatematerials over a predetermined size from entering the reservoir and theoil recirculation means.

A more preferred embodiment of the invention is shown in FIG. 3 whereinparts which are fully equivalent to those in either of FIGS. 1 or 2 havethe same last two digits as those parts, but all parts are labeled withnumbers above 300. This embodiment differs principally from those ofFIGS. 1 and 2 in that convection within the oven is created by rotatingthe foraminous support 314 within the chamber 310 instead of holding thesupport stationary as in FIGS. 1 and 2 and forcibly directing airtherethrough.

As with the embodiment of FIG. 2, the chamber 310 is closed, in thisembodiment having a cover 312 which enables sealing and pressurizing thechamber. Oil or other liquid heat exchange medium is maintained inreservoir 316 and is pumped through conduit 318 by means of draw pipe317 and pump 332 to oil dispersion means 320 having a plurality ofradially extending dispersion conduits 321 therein. The lower portion ofthe chamber 310 is seen to include electrical resistance heatingelements 328 embedded within a ceramic or other material which maintainsgood heat exchange contact with the interior of the chamber and,preferably, the collecter 315 and reservoir 316. Optionally, a separateheating means (not shown) can be employed in reservoir 316.

The foraminous support means 314 is rotatably mounted on a shaft 334which is turned at a desired rate of speed by an electric motor shownschematically as 336. The entire lower portion of the apparatus ismaintained within a housing 338 which can contain suitable controlmeans, not shown, on the exterior thereof.

In the operation of the apparatus shown in FIG. 3, oil is continuouslydispersed from means 321 into the air maintained within the chamber 310.The liquid heat exchange medium contacts by air flow onto the contentsof the support 314 which are maintained in constant rotation by motor336. The motor can be driven at speeds effective to maintain a rapidrelative motion between the air within the chamber and the contents ofthe support 314 to provide the convection heating effect. If desired,the motor 336 can be controlled by means not shown to vary the rate anddirection of rotation of the support 314.

As with the other embodiments, the oil will be supplied at a ratesufficient to fully wet the surfaces of the contents of support 314 suchthat the liquid medium can most effectively be employed to improve theheat transfer from the heating means 328 to the food. A portion of theliquid medium will drip from the contents of the support 314 directlyonto the heated lower portion of chamber 310, be collected in means 315and then passed into reservoir 316 by line 319 for recycle to theprocess or storage until the next cooking operation. Preferably, therate of rotation of support 314 is periodically increased to a rateeffective to cause excess liquid medium to be removed by centrifugalforce onto the interior of the heating chamber 310 for flow downwardlyinto reservoir 316, being heated along the way by heating elements 328.And, after heating is completed, the rate of rotation of support 314 isagain increased, and the pump 332 is stopped, to spin off excess liquidwhich is then collected in reservoir 316 for storage until the nextcooking cycle.

The device shown in FIGS. 4 and 5 is a more preferred arrangementaccording to the present invention. All of the parts in FIGS. 4 and 5are identified with three-digit numbers greater than 400, with all partswhich are equivalent to those shown in previous Figures having the samelast two digits as their respective counterparts.

Referring first to FIG. 5 which shows the apparatus in partial crosssection, there is seen a heating chamber 410 having a cover 412positioned thereon. Within the chamber is a foraminous support 414having a generally circular cross section which decreases from top tobottom, giving a generally rounded shape. The support 414 is rotatablypositioned within the chamber 410 to provide an annular space 450between the support 414 and the interior of the chamber wall 410. At thebottom of the heating chamber is a reservoir 416 having a heat exchangeelement 428 in heat exchange contact therewith. Positioned within theresevoir 416 is an oil dispersion means 420 which in this embodiment isan impeller blade which continuously disperses the liquid heating mediumwhich collects in reservoir 416 and throws the dispersion up through thebottom of the foraminous support 414 and through the annular passage 450between the support 414 and the wall of chamber 410. The impeller 420and the heat exchange element 428 operate much like a scraped surfaceheat exchanger to rapidly reheat the oil for recyclation.

As shown in the Figures, both the impeller means 420 and the foraminoussupport 414 rotate during the heating operation. Because the foraminoussupport 414 is of greater diameter than the impeller 420, and becausethe impeller must operate at a high speed in order to finely dispersethe oil, it is preferred that separate rotational drive shafts beprovided to move these individual elements. Accordingly, acentrally-located shaft 434 is shown fitting into sleeve 452 at thebottom of the foraminous support 414. The shaft 434 is preferablymechanically interlocked by a suitable configuration, not shown, toprevent slippage between sleeve 452 and shaft 434. Positioned exteriorlyof a lower portion of shaft 434 is a rotatable sleeve 460 onto which theimpeller 420 is attached to permit rotation, but also preferably permiteasy removal for cleaning. The sleeve 460 and the shaft 434 are made ofsuitable high-surface-strength materials which permit relative rotationsat different speeds over extended periods of time without excessivewear.

The drawing in FIG. 5 shows a single electric motor means 436 which canbe employed by suitable gearing to drive both shafts 434 and 460 atdifferent rates of speed. However, it is desired to employ twoseparately controlable electric motors. Alternatively, a single,high-speed motor may be directly coupled to shaft 460 for constant speedof rotation of the impeller 420, with the rate of rotation of the shaft434 being varied by means of a magnetic clutch or other suitable device.

Preferably, the rate of rotation of shaft 434 can be varied duringoperation to permit continuous rotation of the foraminous support 414with periodical increases in the rate of rotation to a rate effective tocause excess liquid heat exchange medium to be removed from the articlescontained in the support 414 by centrifugal force. Especially preferredare those arrangements in which the impeller blade 420 can be stopped atthe end of a desired period of heating to terminate the dispersion ofoil within the chamber and onto the food, but which permit rotation ofthe foraminous support 414 at a rate effective to centrifugally remove asignificant portion of the excess cooking medium from the articlescontained within the support 414.

As shown in FIGS. 4 and 5, a lower housing 448 has a control panel 470on the exterior thereof. On the control panel is a control knob 472which has the dual function of a main power switch and rheostat forcontrolling the power supply to heating element 428. Preferably, thecontrol panel will also contain a temperature gauge 474 for morepositive control of temperature within the chamber 410. One or morethermal couples, not shown, can be positioned at strategic locationswithin the chamber 410 to indicate or control the temperature at theselocations. The control panel 470 will also contain speed control buttons476 which can be employed to set the desired speed of rotation for boththe impeller blade 420 and the support 414 as may be desired.

The cover 412 preferably has a downwardly depending outer flange 480 anda rubber or other suitable gasket material 482 positioned on the insideof the flange for contact with an upper flange 484 on the top of thechamber wall 410. Suitable clamping means are preferably provided asshown at 486 in the drawing for locking the cover 412 on top of thechamber 410 to provide the ability to maintain a positive pressurewithin the heating chamber. Preferably, the seal will be effective tomaintain a pressure of from about 1 to about 50 psig during heating, anda pressure relief valve 488 will be provided at the top of the cover 412to permit release of gases in the event of excessive pressure buildup.The pressure relief valve 488 can also be employed to rapidly releasethe pressure upon termination of heating so that the clamping means 486can be removed more quickly. The vent 488 at the top of cover 412 can befitted with an oil trap and can be made adjustable if desired.

The drawing in FIG. 5 shows the relative placement of the parts of theapparatus in an exploded view, emphasizing the simplified cleanup whichcan be expected by the home cook when employing the apparatus. Inessence, three main parts, the lower chamber portion 410, the foraminoussupport 414 and the cover portion 412 are removed from the base 448 forcomplete immersion in soapy water to effect rapid cleanup. The baseremains clean and free of cooking mess.

The temperature indicator 474 on the control panel 470 can be employedto register the temperature internally of a food article which is cookedvia holding the support member 414 stationary. Convection within theheating chamber 410 can be effected without rotation of the support 414by properly designing the impeller to draw air up or down essentiallythrough the foraminous support and then direct it outwardly through theannular channel 450 while dispersing the heated oil. The air flowthrough channel 450 would then impinge off the cover 412 and be againdrawn through the contents of the support 414 and the support itself forredistribution through channel 450.

According to one exemplary mode of operating in apparatus as shown inFIGS. 4 and 5, the cover 412 and the foraminous support 414 are removedand the reservoir 416 is filled with an appropriate amount of oil,typically one half cup or less. Then, control 472 is set to achieve anappropriate temperature of about 400° F. for frying. Next, the basket414 is replaced and filled with food such as chicken having a battercoating thereon. The lid 412 is then replaced and sealed by means ofclamps 486. When the oil has reached the appropriate temperature, therotation of the outer shaft 460 with the associated impeller blade 420is begun to disperse hot oil throughout the chamber 410. Next, rotationof the inner-shaft 434 and the basket 414 are begun to provideappropriate convective hot air flow containing finely dispersed hot oil,relative to the chicken maintained within the basket 414.

After a desired period of time, typically about 2 minutes, the speed ofrotation of the basket is increased to a rate effective to remove excessoil from the chicken by centrifugal force. Rapid rotation is terminatedafter about 15 seconds and cooking is continued for an additional 2 to10 cycles of rotation at different speeds until cooking is completed.After cooking is completed, the rotation of shaft 460 and the impellerblade 420 is terminated and the shaft 434 is again rotated at high speedfor an additional few seconds to spin excess oil from the chicken tomake it ready for consumption. Finally, the clamps 486 are loosened andthe cover 412 is removed.

Another advantage of the apparatus of the invention is that the food canbe maintained within the basket 414 with the cover on for continuedwarming for any desired period of time prior to serving, unlikeconventional frying which requires removing the fried foods from thecooking container which typically contains large amounts of fat at thebottom. If needed, a brief period of cooking can be used to reheat foodsthat have become too cool for proper serving. Thus, according to thepresent invention, not only is the fear of frying overcome to a largeextent, but the home cook's requirement for timing each of theindividual items on the menu is made less critical.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of FIG. 6 is the most preferred. According to thisembodiment, a flow of heat exchange fluid (shown by arrows) isestablished which, due to its generation by impeller means 620 withinthe closed chamber 610 at a location accentrically positioned relativeto the axis of rotation of the support 614, uniformly contacts thematerial being heated as it is being rotated by the support means. Theaxis of the support 614 and the impeller means 620 are spaced from eachother effectively to create a flow of heat exchange fluid which passesup through the support at one side of its center and down through it atan opposed side. This flow, created by the impeller means, is in a planewhich intersects the plane of movement of the support. The flow of heatexchange fluid substantially totally intersects the plane of thematerial to be heated.

By providing this type of flow, hot spots and dead spaces are greatlyreduced--giving a product which is uniformly heated. Fried foods, whichare among the most sensitive to uniform heating, will show a uniformlydeveloped fried crust. Use of the apparatus for other cooking processeswill show improvements also, though they may be less noticeable tocasual observation.

The heating chamber 610 is shown in FIG. 6 as the enclosed space betweenchamber liner 611 and cover 612. The chamber liner 611 is preferablyremovable in one piece from base 648. The liner preferably has anon-stick coating (not shown). The support or basket 614 is rotatableabout an axis defined as shaft 634 which is driven by an electric motor(not shown). The motor is operated in known manner, preferably bysuitable controls (note control panel 670) giving a wide variation inspeeds ranging from zero to 100 or more rpm. In some cases, speeds offrom about 1/2 to about 10 rpm will be preferred for many cookingoperations to provide a desirable variation in the location ofindividual items to be heated relative to the flow of heat exchangefluid while not causing movement of the items within the support 614.

Accentrically located from shaft 634 is an axis defined by shaft 660which rotatably supports impeller means 620. Also located on shaft 660is a dispersing blade 621 or other device including ultrasonics, whichfunctions to break up liquids into a fine dispersion for circulationthrough the chamber by a flow of air created by impeller means 620. Asecond electric motor (not shown) is configured in conventional mannerto rotate shaft 660 and impeller means 620 at a wide range of speeds toestablish and maintain a desired flow of heat exchange fluid within thechamber 610. Low speeds up to about 10-25 rpm will be effective for somecooking methods such as slow cooking wherein an aqueous sauce or gravyfills chamber 610 sufficiently to cover solid food maintained in thesupport 614. In other cases, particularly dynamic frying, wherein acooking fat or oil is dispersed in a flow of air, higher impeller speedssufficient to develop air flow rates conventional for convection heatingwill be desired. Very high speeds, effective to stir and toss foods suchas cut vegetables and meat will also be desirable for cooking processessuch as stir frying. For stir frying, it will be desirable to properlyconfigure the support 614 and the cover 612 or a separate basket cover(not shown) to retain the rapidly moving food pieces within the support614. Also, intermediate speeds may be effective for steaming, drying andother processes.

The liner 611 of chamber 610 is configured to slope toward impellermeans 620 so that liquid heat exchange fluid contacting the wall will becollected there for recirculation. Also, preferably located in the lowerportion of liner 611 are a plurality of electric heating means 628 forheating the heat exchange fluid to the desired temperature for transferto the material being heated.

As will be apparent from the above description, the apparatus can beemployed for heating foods other than with cooking oil and other than toprovide a fried texture. For example, by employing water and suitablylow temperature within the cooking chamber, the apparatus can providethe same heating advantages as boiling, but without great losses ofvaluable nutrients or flavors to the cooking water. Similarly, a bastingsauce such as barbecue sauce can be employed. The basting sauce can beused in small amounts and finely dispersed in a circulating flow, or canbe present in large quantities and slowly circulated in bulk to slowcook the food. Also the apparatus can be used to stir fry foods usingsmall amounts of very hot oil. And, if desired, the apparatus can beemployed to steam foods in both a conventional fashion and an enhancedconvection steaming mode, thus making the apparatus more versatile anduseful to the home cook. Also, by employing no liquid medium butcirculating only hot air and exhausting a portion of it, foods can beefficiently convection heated or air dried. By enabling the use of theapparatus for a wide variety of common cooking procedures, and therebyincreasing its utility, the home cook's familiarity with the apparatusand its advantages will become more pronounced due to more frequent use.And, special foraminous supports of particular shapes for particularfood products can be designed to take advantage of this versatility.

The above description has been for the purpose of teaching the person ofordinary skill in the art how to use the present invention. Applicantdid not intend to describe each and every obvious modification of theinvention which will become apparent to skilled workers upon reading thedescription. It is intended, however, that all such obviousmodifications and variations be included within the scope of theinvention which is defined by the following claims.

I claim:
 1. A heating apparatus which comprises: a heating chamber, aforaminous support means for holding material to be heated within saidchamber, means for creating a flow of hot air in proximity to thesupport means, means for introducing a dispersed liquid heat exchangemedium into the air within the chamber, means within said chamber forheating said air and said dispersed liquid heat exchange medium, meansfor collecting and reheating liquid heat exchange medium having drippedfrom said material, and means for redispersing said liquid heat exchangemedium into said air flow.
 2. A heating apparatus according to claim 1which further includes means for sealing the heating chamber to maintaina positive pressure therein.
 3. A heating apparatus according to claim 1wherein the means for creating a flow of hot air in proximity to thesupport means comprises means for rotating the support means within thechamber.
 4. A heating apparatus according to claim 1 wherein said meansfor collecting and reheating comprises reservoir means for collectingliquid heat exchange medium during heating.
 5. A convection heatingapparatus according to claim 1 wherein said means for collecting andreheating comprises a heated reservoir means for holding liquid heatexchange medium at the bottom of the chamber and impeller meanspositioned within the reservoir means for dispersing the heat exchangemedium.
 6. A convection heating apparatus according to claim 1 whereinthe means for creating a flow of hot air in proximity to the supportmeans comprises an electrical resistance heater means and an impellermeans.
 7. A convection heating apparatus according to claim 6 whereinthe foraminous support means has a generally circular cross sectionwhich decreases from top to bottom to provide a generally rounded shape,and the support means is positioned within the heating chamber toprovide an annular space between the support means and the interiorsurface of the heating chamber.
 8. A convection heating apparatusaccording to claim 7 wherein heating means are positioned in heatexchange contact with the reservoir and the annular space, to heatliquid heat exchange medium contained in the reservoir and the air inthe annular space.
 9. A convection heating apparatus according to claim1 which further includes means for rotating the support at a pluralityof rates, at least one being effective to cause excess heat exchangemedium to be spun from the articles being heated.